My friend stole my ipod nano!!?

ok i lost my ipod nano in 1st period in cl and my friend was digging my bag.then she has an ipod and she said its her cousin's,her cousin got a whole bunch of iPods and she will ask her cousin if she can get an extra ipod for me,which is the one that her cousin borrowed to her. she told me the ipod she got from her cousin is like mine, its purple. but she never shows it when i was with her and she hides it in her bra. then i told another friend,she has the 6th period with her so i told her to check the serial number if she can. and that friend wrote down the SN and checked mine, its totolly the same number, and i know its mine. so i asked her but she does not admit and she said she dosen't have it today and she said she will give her cousin's ipod to me on friday so i can check the number. i was so stupid i shouldnt have told her i should just tell the dean yesterday because she had it with her yesterday and now she is not getting it back i have no proof if she change the ipod on friday. i didnt tell my parents yet cause they are going to get pissed off. and she was still like im helping you i will let my cousin get another one for you how would you think i took it?if the ipod is not y ours i want you to appologize! she is so fake and i know she would show me another ipod on friday! what can i do? i know she has it but i cant have it back?!